Comparison of methods for determining the partition coefficient of gadolinium in the myocardium using T1 mapping.

PURPOSE: To develop and validate modified Look-Locker (MOLLI) protocols to generate myocardial T1 maps within clinically acceptable breath-hold durations and to compare partition coefficients (λ) of gadolinium (Gd)-DTPA determined from either bolus injection (BI) or continuous infusion (CI) techniques. MATERIALS AND METHODS: T1 mapping was performed in phantoms and in 10 volunteers on a 1.5T scanner using the standard (3-3-5) MOLLI technique and two MOLLI schemes with shorter breath-hold durations. Imaging was performed precontrast and every 5 minutes following a bolus of 0.1 mmol/kg Gd-DTPA and a 15-minute delayed continuous infusion of 0.001 mmol/kg Gd-DTPA until equilibrium T1 in the myocardium was achieved to enable direct comparison of T1 relaxation times between techniques and λ's between the BI and CI methods. RESULTS: There was good agreement of T1 values between the 3-3-5 standard MOLLI protocol and the modified 3-5 MOLLI protocol in both phantom studies over a range of heart rates and in human subjects. Both MOLLI protocols produced similar measurements of λ using both the BI and CI methods. CONCLUSION: A reduced breath-hold MOLLI T1 mapping protocol combined with the BI method can accurately characterize T1 and λ in clinically applicable breath-hold durations without requiring a long equilibrium phase infusion.

Reproducibility of rest and exercise stress contrast-enhanced calf perfusion magnetic resonance imaging in peripheral arterial disease.

BACKGROUND: The purpose was to determine the reproducibility and utility of rest, exercise, and perfusion reserve (PR) measures by contrast-enhanced (CE) calf perfusion magnetic resonance imaging (MRI) of the calf in normal subjects (NL) and patients with peripheral arterial disease (PAD). METHODS: Eleven PAD patients with claudication (ankle-brachial index 0.67 ±0.14) and 16 age-matched NL underwent symptom-limited CE-MRI using a pedal ergometer. Tissue perfusion and arterial input were measured at rest and peak exercise after injection of 0.1 mM/kg of gadolinium-diethylnetriamine pentaacetic acid (Gd-DTPA). Tissue function (TF) and arterial input function (AIF) measurements were made from the slope of time-intensity curves in muscle and artery, respectively, and normalized to proton density signal to correct for coil inhomogeneity. Perfusion index (PI) = TF/AIF. Perfusion reserve (PR) = exercise TF/ rest TF. Intraclass correlation coefficient (ICC) was calculated from 11 NL and 10 PAD with repeated MRI on a different day. RESULTS: Resting TF was low in NL and PAD (mean ± SD 0.25 ± 0.18 vs 0.35 ± 0.71, p = 0.59) but reproducible (ICC 0.76). Exercise TF was higher in NL than PAD (5.5 ± 3.2 vs. 3.4 ± 1.6, p = 0.04). Perfusion reserve was similar between groups and highly variable (28.6 ± 19.8 vs. 42.6 ± 41.0, p = 0.26). Exercise TF and PI were reproducible measures (ICC 0.63 and 0.60, respectively). CONCLUSION: Although rest measures are reproducible, they are quite low, do not distinguish NL from PAD, and lead to variability in perfusion reserve measures. Exercise TF and PI are the most reproducible MRI perfusion measures in PAD for use in clinical trials.

Non-invasive imaging and monitoring cardiotoxicity of cancer therapeutic drugs.

Cardiotoxicity due to administration of cancer therapeutic agents such as anthracyclines and herceptin are well described. Established guidelines to screen for chemotherapy-related cardiotoxicity (CRC) are primarily based on serial assessment of left ventricular (LV) ejection fraction (EF). However, other parameters such as LV volume, diastolic function, and strain may also be useful in screening for cardiotoxicity. More recent advances in molecular imaging of apoptosis and tissue characterization by cardiac MRI are techniques which might allow early detection of patients at high risk for developing cardiotoxicity prior to a drop in EF. This comprehensive multi-modality review will discuss both the current established imaging techniques as well as the emerging technologies which may revolutionize the future of screening and evaluation for CRC.

Heparin-induced thrombocytopenia (HIT) causing pulmonary emboli during coronary intervention.

Thrombotic complications of heparin-induced thrombocytopenia (HIT) can be devastating if not recognized and treated promptly. We describe an unusual case of rapid-onset HIT resulting in massive-bilateral pulmonary emboli in a 70 year-old man who developed chest pain during elective percutaneous coronary intervention (PCI). The diagnosis was made the following day after persistent chest pain and laboratory work demonstrating a new thrombocytopenia, a mildly elevated troponin, and positive DIC panel led to confirmatory imaging tests. HIT-related thrombosis should be considered in the differential diagnosis of chest pain in patients undergoing PCI.

Arterial spin labeling MR imaging reproducibly measures peak-exercise calf muscle perfusion: a study in patients with peripheral arterial disease and healthy volunteers.

OBJECTIVES: This study hypothesized that arterial spin labeling (ASL) magnetic resonance (MR) imaging at 3-T would be a reliable noncontrast technique for measuring peak exercise calf muscle blood flow in both healthy volunteers and patients with peripheral arterial disease (PAD) and will discriminate between these groups. BACKGROUND: Prior work demonstrated the utility of first-pass gadolinium-enhanced calf muscle perfusion MR imaging in patients with PAD. However, patients with PAD often have advanced renal disease and cannot receive gadolinium. METHODS: PAD patients had claudication and an ankle brachial index of 0.4 to 0.9. Age-matched normal subjects (NL) had no PAD risk factors and were symptom-free with exercise. All performed supine plantar flexion exercise in a 3-T MR imaging scanner using a pedal ergometer until exhaustion or limiting symptoms and were imaged at peak exercise with 15 averaged ASL images. Peak perfusion was measured from ASL blood flow images by placing a region of interest in the calf muscle region with the greatest signal intensity. Perfusion was compared between PAD patients and NL and repeat testing was performed in 12 subjects (5 NL, 7 PAD) for assessment of reproducibility. RESULTS: Peak exercise calf perfusion of 15 NL (age: 54 ± 9 years) was higher than in 15 PAD patients (age: 64 ± 5 years, ankle brachial index: 0.70 ± 0.14) (80 ± 23 ml/min - 100 g vs. 49 ± 16 ml/min/100 g, p < 0.001). Five NL performed exercise matched to PAD patients and again demonstrated higher perfusion (84 ± 25 ml/min - 100 g, p < 0.002). As a measure of reproducibility, intraclass correlation coefficient between repeated studies was 0.87 (95% confidence interval [CI]: 0.61 to 0.96). Interobserver reproducibility was 0.96 (95% CI: 0.84 to 0.99). CONCLUSIONS: ASL is a reproducible noncontrast technique for quantifying peak exercise blood flow in calf muscle. Independent of exercise time, ASL discriminates between NL and PAD patients. This technique may prove useful for clinical trials of therapies for improving muscle perfusion, especially in patients unable to receive gadolinium.

Cardiovascular magnetic resonance: applications in daily practice.

Over the last 10 years, the development of newer pulse sequences and applications in new clinical areas has enabled cardiovascular magnetic resonance to emerge as a powerful tool for the physicians to both diagnose and guide treatments of various cardiac pathologies. The greatest strengths of cardiovascular magnetic resonance include the assessment of ischemia and viability, evaluation of nonischemic cardiomyopathies, including myocarditis, pericardial disease, congenital heart disease, and tissue characterization of cardiac masses.